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Team reveals protein complex structure through repeated experiments

Legionnaires’ disease, first reported in the United States, is an infectious disease that can be fatal. About 200 attendees of a 1976 American Legion convention in Philadelphia were infected, and 28 of them died. In Korea, 30 ICU patients at a general hospital in Seoul contracted the disease in 1984, and among them, 4 died. Outbreaks have been detected every summer, but there is no vaccine available to date. The team, led by Professor Byung-Ha Oh, became the world’s first to reveal the structure of the Legionella pneumophila secretion system, which causes Legionnaires’ disease, thereby laying a foundation for the development of antibiotics.

Legionella pneumophila protein complex structure unveils method of recognizing effector proteins

Legionnaires’ disease is a Class 3 infectious disease in Korea. While multi-drug resistant strains have not been discovered, the disease-causing Legionella pneumophila is known as a highly virulent athogen. New antibiotics are required when a pathogen gains antibiotic resistance. Similar to other pathogens, the protein secretion mechanism of Legionella pneumophila involves two steps. First, the system recognizes effector proteins from among thousands of bacterial proteins. Next, it
secrets them outside of cells. The research team revealed the entire structure of the type VI coupling protein complex, which is responsible for the first step. They found that six different proteins (DotL, DotN, ImsS, ImsW, LvgA, DotM) form the core of the protein complex. By reporting the coupling of the complex to effector proteins, the team identified the part of the protein complex that recognizes and selects effector proteins.

“Basis for development of antibiotics that are not toxic to humans”

Professor Byung-Ha Oh said, “The bottom of the complex selectively recognizes effector proteins, and the ATPase domain at the top processes the structure into a linear chain, releasing it through the central path. The released chain is transferred to another protein complex, and eventually
secreted outside cells.” The team repeated their experiments to ensure high accuracy, and found that the surface of the binding site is concave and
comprised of hydrophobic amino acids. Antibiotics effective against Legionella pneumophila may be developed by finding molecular compounds that bind strongly to the surface of effector proteins. The results are expected to serve as a basis for follow-up studies on the development of antibiotics that are not toxic to humans. The paper was published in the international journal, Nature Communications, in May 2020.

Prof. Byung-Ha Oh
2020 KI Annual Report

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